Sediment Flow Research Articles

Environmental drivers of seasonal and hourly fluxes of methane and carbon dioxide across a lowland stream network with mixed catchment

Streams serve as open windows for carbon emissions to the atmosphere due to the frequent supersaturation of carbon dioxide (CO2) and methane (CH4) that originates from large carbon input during runoff and associated in-stream processes. Due to the high spatial and temporal variability of the underlying environmental drivers (e.g., concentrations of dissolved CO2 and CH4, turbulence, and temperature), it has remained difficult to address the importance and upscale the emissions to annual whole-system and regional values. In this study, we measured concentrations and calculated emissions of CO2 and CH4 at diel and seasonal scales at 15 stations in a 1.4 km2 stream network that drains a mixed lowland catchment consisting of agriculture (210 km2), forest (56 km2), and lakes, ponds, and wetlands (22 km2) in the upper River Odense, Denmark to evaluate environmental drivers behind the spatiotemporal variability. We used automatically venting floating chambers to calculate hourly diffusive fluxes of CO2 and CH4 and CH4 ebullition. We found: 1) highly supersaturated CO2 and CH4 concentrations (median: 175 and 0.33 µmol L−1, respectively) and high diffusive fluxes of CO2 and CH4 (median: 3,608 and 19 µmol m−2 h−1, respectively); 2) lower daytime than nighttime diffusive emissions of CO2 in spring and summer, but no diel variability of CH4; 3) higher concentrations and emissions of CH4 at higher temperatures; and 4) higher emissions of CH4 at stations located in sub-catchments with higher agricultural coverage. Ebullition of CH4 peaked at two stations with soft organic sediment and low summer flow, and their ebullition alone constituted 30% of total annual CH4 emissions from the stream network. Mean annual CO2 emissions from the hydrological network (37.15 mol CO2 m−2 y−1) exceeded CH4 emissions 100-fold (0.43 mol CH4 m−2 y−1), and their combined warming potential was 1.83 kg CO2e m−2 y−1. Overall, agricultural sub-catchments had higher CH4 emissions from streams, while lakes and ponds likely reduced downstream CH4 and CO2 emissions. Our findings demonstrate that CO2 and CH4 emissions data at high spatial and temporal resolution are essential to frame the heterogeneous stream conditions, understand gas emissions regulation, and upscale to annual values for hydrological networks and larger regions.

Modeling sediment flow analysis for hydro-electric projects using deep neural networks

Modeling sediment flow analysis for hydro-electric projects using deep neural networks

Spatial Scale Effects on Erosive Runoff and Sediment Flow Behavior on Loessial Slopes: An Erosive Energy Basis

ABSTRACTRunoff erosion response associated with sediment transport as influenced by erosive energy variability is a highly scale‐dependent process. Identifying the spatial scale effect on erosive runoff energy is important to understand the spatial pattern of sediment flow behavior across various sites. This issue was resolved by establishing thresholds for erosive runoff based on frequency analysis, which considered four selected threshold parameters: runoff duration (T), stream power (ω), stream energy factor (SE), and area‐specific sediment yield (SSY). Based on these thresholds, 77 erosive events were identified and separated from nonerosive events for further analysis of energy–sediment relationships. The threshold for T was roughly constant at hillslopes but rapidly increased at the entire slope. Thresholds for ω and SE exhibited positive linear relationships with the plot area, whereas the threshold for SSY showed a general increasing trend along the downslope direction. The R2 values of erosive energy–sediment relationships at inter‐ and intra‐event time scales were generally higher for erosive events than for nonerosive events. The sediment delivery capacity (Cd) for erosive runoff ranged from 0.075 to 0.115 kg·m·J−1. It demonstrated an initial increase followed by a subsequent decrease from the upper hillslope to the entire slope. Conversely, Cd for nonerosive runoff increased with the rise in plot area, and it ranged from 0.053 to 0.083 kg·m·J−1. The sediment‐increasing capacity (Ci) for erosive runoff ranged from 0.43 to 4.47 kg·m−2·W−1, whereas Ci for nonerosive runoff varied from 3.39 to 17.6 kg·m−2·W−1. The sediment reduction benefit by regulation unit stream energy factor varied from 5% at the entire slope to 65% at the upper hillslope. Therefore, anti‐erosion measures should be implemented at the upper hillslope to prevent nonerosive runoff from becoming erosive runoff.

Impacts of LULC and climate change on runoff and sediment production for the Puyango-Tumbes basin (Ecuador-Peru)

Climate change will cause alterations in the hydrological cycle, a topic of great relevance to the scientific community due to its impacts on water resources. Investigating changes in hydrological characteristics at the watershed level in the context of climate change is fundamental for developing mitigation and adaptation strategies against extreme hydrological events. This study aimed to analyze the impacts of climate change on flow and sediment production in the Puyango-Tumbes watershed. Projected climate data from CMIP6 were used, corrected through a bias adjustment process to minimize discrepancies between model data and historical observations, ensuring a more accurate representation of climate behavior. The analysis combined two representative climate change scenarios (SSP2-4.5 and SSP5-8.5) with two land use and land cover (LULC) scenarios: (a) an optimistic scenario with reduced anthropogenic effects (LULC_1985) and (b) a pessimistic scenario reflecting future impacts (LULC_2015). The SWAT model estimated future flow and sediment production for two periods (2035-2065 and 2070-2100), following model calibration and validation against the reference period 1981-2015 at three hydrometric stations: Pindo, Puyango, and El Tigre, located in Ecuador and Peru. The simulations revealed a significant increase in sediment generation under the pessimistic scenario SSP5-8.5, followed by SSP2-4.5, while lower sediment yields were observed in the optimistic scenarios. Even in the best-case scenario (optimistic SSP2-4.5), sediment yields remained substantially higher than the reference conditions. Additionally, higher flows were anticipated in some scenarios, with the El Tigre station in the lower watershed being the most affected area. These findings underscore the high probability of more frequent flooding events due to increased sediment yields and flow variability. The results highlight the urgent need for implementing adaptation measures, such as improved land use management and hydrological infrastructure, to enhance social resilience and mitigate the impacts of climate change in the watershed.

Validation of Soil Detachment Rate Equations on Spring Thaw Period Slopes: Insights From Sediment Concentration and Transport Capacity

AbstractSoil detachment plays a central role in the formulation of soil erosion models, particularly for the simulation and prediction of erosion in cold climates during the thaw period. This research attempts to elucidate the mechanisms of soil detachment on spring thaw period slopes through comprehensive flume experiments, coupled with the application of rare earth element (REE) tracer, investigating the relationships between soil detachment rates, sediment concentration and sediment transport capacity. Observations indicate a nuanced response of soil detachment rate and sediment concentration to scour duration, characterized by an initial increase, subsequent decrease and eventual equilibrium. As thaw depth increases, the primary source of eroded sediment gradually shifts from the upper slope to the mid‐slope. Soil detachment rate was affected by sediment concentration, flow discharge, slope gradient, thawing depth, and slope positions. Furthermore, our analysis reveals a power function relationship (R2 = 0.846) between soil detachment rate, effective shear stress, and sediment transport rate and capacity. These results provide valuable insights into the modeling and prediction of soil erosion processes on brown soil slopes subjected to spring thaw period cycles.

Numerical investigation on the evolution process of hydraulic transport and overcurrent blockage of silted urban rainwater pipelines: An approach based on computational fluid dynamics and discrete element method

During urban flood events, the effect of urban rainwater pipeline siltation on overflow and stagflation intensifies the severity of flood disaster. However, the dynamic coupling mechanism of pipeline sedimentation and water flow is still unclear. To investigate the influence of two-phase flow on the hydraulic transport of siltation particles in rainwater pipelines, the numerical simulation model based on computational fluid dynamics (CFD) and discrete element method (DEM) is constructed. Then, the transient continuity governing equation and conservation equation of momentum are formulated to provide dynamic guidance and boundary constraint for CFD-DEM simulation. On this basis, the optimal drag force model and measurement method of equivalent siltation degree of pipeline are proposed and nested with CFD-DEM, and then, a high resolution numerical simulation model of pipeline sedimentation is formulated. The results show that the siltation degree affects the efficiency of drainage pipeline to a degree of 47%, which is much greater than the degree of influence of 33% for siltation length and 18% for slope. When the siltation degree is 0.1, the thickness of the silted bed surface under the influence of water flow scour is reduced by 33%. It revealed that the influence degree of siltation degree and flow rate was 168% and 20%, respectively, which was much larger than that of siltation length and slope. This study can provide technical support for subsequent pipeline cleaning and maintenance as well as flood prevention and mitigation.

Seabed Seismographs Reveal Duration and Structure of Longest Runout Sediment Flows on Earth

AbstractTurbidity currents carve the deepest canyons on Earth, deposit its largest sediment accumulations, and break seabed telecommunication cables. Powerful canyon‐flushing turbidity currents break sensors placed in their path, making them notoriously challenging to measure, and thus poorly understood. This study provides the first remote measurements of canyon‐flushing flows, using ocean‐bottom seismographs located outside the flow's destructive path, revolutionizing flow monitoring. We recorded the internal dynamics of the longest sediment flows yet monitored on Earth, which traveled >1,000 km down the Congo Canyon‐Channel at 3.7–7.6 m s−1 and lasted >3 weeks. These observations allow us to test fundamental models for turbidity current behavior and reveal that flows contain dense and fast frontal‐zones up to ∼400 km in length. These frontal‐zones developed near‐uniform durations and speeds for hundreds of kilometres despite substantial seabed erosion, enabling flows to rapidly transport prodigious volumes of organic carbon, sediment, and warm water to the deep‐sea.

Numerical investigation on erosion characteristics of elevated pile cap in high concentration sediment flow environment

The objective of this investigation is to study the erosion process and characteristics of elevated pile cap in high concentration sediment flow environment, taking into account the influence of multiple factors. Firstly, a three-dimensional model of elevated pile cap was established and used for numerical simulation of erosion. Subsequently, the validity of the elevated pile cap erosion numerical model was corroborated through a comparison with the results of existing physical model tests. Finally, the influence of hydrological conditions, structure geometric characteristics, and material properties on the erosion characteristics of the elevated pile cap were investigated. The numerical results demonstrate that the sand content, flow velocity and pile longitudinal clearance diameter ratio are positively correlated with the abrasion thickness and erosion rate of the elevated pile cap. The pile diameter, the pile transverse clearance diameter ratio, and the compressive strength have a negative correlation with the abrasive thickness and erosion rate of the elevated pile cap. When the particle diameter increases from 0.2 to 2.0 mm, the erosion rate of the pile foundation first decreases and then increases. If the bearing platform is not fully submerged, the erosion rate of the elevated pile cap decreases with the increase of water depth. As the water gradually submerges the bearing platform, the erosion rate of the pile foundation increases with the increase of water depth. And with the change of impact angle, the shielding effect of the front pile on the back pile will also change, which has a great influence on the downstream piles erosion. This study not only enriches existing erosion theories but also guides erosion protection of the elevated pile cap.

Exploring changes in epibenthic food web structure after implementation of a water-sediment regulation scheme

The water-sediment regulation scheme (WSRS) in the Yellow River is a large-scale initiative to artificially regulate the flow of sediment to the sea, thereby increasing the flood-carrying capacity of the riverbed and reservoirs. Currently, systematic studies on ecological impacts of WSRS at ecosystem-level are still insufficient. This limitation hampers the pursuit of a ‘green’, healthy, ecosystem and sustainable fisheries. This study constructed the topological structure of food webs in the Yellow River Estuary (YRE) before, during, and after implementation of the WSRS, analyzing changes in food web complexity and key species based on fishery independent data collected in June, July, and August 2023. The results showed decreases from 59 to 52 in the number of trophic species, and from 539 to 395 in the number of feeding relationships after WSRS implementation. Increased node density, decreased link density, and decreased structural complexity index also indicated a simplification of the YRE food web structure after WSRS implementation. The relatively low value of the characteristic path length indicated that the YRE food web has high connectivity with short path lengths of trophic interaction. Based on the ranking of various topological indices, Japanese seabass (Lateolabrax japonicus) and mantis shrimp (Oratosquilla oratoria) persisted as the key species. Our research revealed limited potential ecological effects that WSRS may have on the YRE food web over a short period. The effects did not persist, and omnivorous key species were identified as being critical in contributing to overall system resilience. These omnivores with high complexity, connectivity and low path lengths allowed the food web to quickly dissipate the exogenous disruption from the WSRS. This provides a theoretical basis for assessing the future ecological health and scientific management of YRE fisheries and similar large estuaries for which sediment transport mitigation is under consideration.

Bedform development in confined and unconfined settings of the Carchuna Canyon (Alboran Sea, western Mediterranean Sea): An example of cyclic steps in shelf-incised canyons

Newly acquired high-resolution multibeam bathymetry in combination with sub-bottom acoustic profiles, surficial sediment samples, and three-dimensional flow simulations made possible the characterization of bedforms along the axial channel and depositional lobe of the shelf-incised Carchuna Canyon (Alboran Sea, western Mediterranean Sea). This study aims to describe the erosional and depositional bedforms in confined and unconfined settings of the Carchuna Canyon in order to determine the genetic constraints on sedimentary processes leading to bedform development along the canyon in recent times.The straight Carchuna Canyon, deeply incised in the shelf up to 200 m off the coastline, hosts: (1) crescentic-shaped bedforms (CSBs) that exhibit distinctive crest concavities, asymmetries, and lengths along the axial channel; (2) continuous lateral levees and; (3) a channel bend with three depressed stretches of the levee crest that are less than 20 m high. A set of concentric sediment waves and two scour trails were identified proximal to the channel bend over an overbank deposit east of the Carchuna Canyon. Four acoustic units with distinct acoustic facies were defined along the sediment wave field. The sediment transport simulation shows the highest flow velocities along the Carchuna Canyon thalweg, while over the overbank deposit the highest velocity values occur along the top of the bedform crests, with the higher Froude values being found over bedform lee sides.The occurrence of CSBs along the canyon axial channel suggests the imprint of confined sediment-laden gravity flows descending from the canyon head and exhibiting a flow variability along the canyon induced by local variations of slope gradient and/or sediment concentration. A spatial relationship is identified between the development of sediment waves over the overbank deposit and lowered levee crest heights at the channel bend. In contrast, more energetic downstream turbiditic flows exceed the levee crest at the channel bend, focusing the overflow and promoting erosion of the overbank deposit, thereby generating the scour trains. Based on the recent history of overbank deposition, two alternating scenarios of flow behavior can be interpreted. In a high-density turbidity current setting, erosion would prevail along the axial channel. Widespread spillover flows of coarse-grained sediments would occur in both levees, forming heterogeneous sedimentary patterns that change downslope within the depositional lobe due to lesser turbulence of spillover turbidity currents and gentler slope gradients. In contrast, in a low-density turbidity current setting, turbidity currents flowing along the Carchuna Canyon would form depositional bedforms in the axial channel, while spillover processes would be localized at the channel bend, forming either depositional or erosional bedforms over the depositional lobe according to the frequency, magnitude and focusing of turbiditic flows.

The Regional Scale of Landscape Planning: the Possibilities for Measuring the Effectiveness of Nature-Based Solutions

Aim: The aim of this study is to investigate the measurement of landscape integrity based on ecological support processes in the Federal District, with the aim of defining a multi-scalar and multi-functional Regional Green Infrastructure Network (IVR) based on Nature-Based Solutions (NBS). Theoretical Framework: This topic presents the main concepts and theories that underpin the research. Landscape Ecology, Restoration Ecology, Green Infrastructure and Geodesign stand out, providing a solid basis for understanding the research context. Method: The methodology adopted for this research comprises the analysis of ecological support processes in the landscape, using the multispectral “CO2flux” index, related to the photosynthetic efficiency of vegetation and a proxy for energy, carbon and biomass inputs, which, together with the “Topographic Wetness Index”, related to the flow and accumulation of water and sediment in the landscape, provided the basis for the elaboration of a Geodesign process. Data was collected using multispectral satellite scenes - “Landsat 8”, collected during the dry season. Results and Discussion: The results obtained revealed the design of a mosaic of “hotspots”, corridors and patches that consolidates and intensifies carbon flows in the Federal District's landscape, with positive impacts on territorial resilience. In the discussion section, these results are contextualized in the light of the theoretical framework, highlighting the implications and relationships identified. Possible discrepancies and limitations of the study are also considered in this section. Research Implications: The practical and theoretical implications of this research are discussed, providing “insights” into how the results can be applied, or how to influence practices in the field of landscape planning. These implications can cover the design of Nature-Based Solutions at a regional scale, climate mitigation and adaptation actions for territories, and people's access to ecosystem services. Originality/Value: This study contributes to the literature by proposing the design of a regional network of green infrastructures based on the analysis of the flow of ecological support processes in the landscape, considering different demands and goals for environmental recovery. The relevance and value of this research is evidenced by the possibility of planning and designing mosaics in the landscape based on the identification of networks with greater potential for the provision of ecosystem services and, consequently, for the adaptation and mitigation of territories to climate impacts and those resulting from human occupation.

Insights into surrogate respiratory droplet behaviour on inclined surfaces: Implications for disease transmission

Disease transmission via fluid ejections from infected individuals presents a significant public health challenge. The ejected droplet frequently lands on substrates with varying orientations, including horizontal, vertical, and inclined. However, the behaviour of disease-causing droplets on inclined substrates remains unexplored. Recent research has demonstrated that droplet evaporation, flow, and colloidal deposition are significantly altered when surfaces are inclined. Changes in contact angle impact evaporative flux and induce flow between the top and bottom edges of the droplet. This study examines the behaviour of simulated respiratory droplets containing NaCl, mucin, and micrometer-sized particles as pathogen surrogates, focusing on substrate inclinations of 0°, 45°, and 90° on glass surfaces. As respiratory droplets evaporate, their solute concentration rises, altering both surface tension and viscosity. The study explores the coupled effects of solute concentration variations and asymmetric evaporative flux at varying relative humidity conditions and droplet volumes. The presence of salt and mucin induces Marangoni flow, potentially altering evaporation, flow patterns, and deposition dynamics. Additionally, sedimentation flow influences crystal nucleation sites and precipitation patterns. Results reveal unprecedented crystallization dynamics on inclined substrates, with notable differences in nucleation and growth based on the angle of inclination. Optical profilometry and confocal microscopy further show that surrogate bacterial particles accumulate excessively at the bottom edge of inclined droplets, suggesting an elevated risk of pathogen survival on inclined fomites. These findings highlight the critical importance of considering substrate orientation in understanding the transmission of disease through surface-bound droplets, offering insights that could inform public health strategies.

The impact of changes in water–sediment relationships at river confluences on the evolution of river bars

The confluence of tributaries and the main stream affects riverbed siltation and alters the upstream water–sediment relationships and flow structure of the main stream by adding additional flow. The relationship between these changes and the evolution of river bars, however, is yet to be fully understood. In this study, the areas of the river bars were extracted from Landsat image and analyzed using soft clustering to identify evolutionary patterns of the bars at the confluence of the Fen River (FR) and Yellow River (YR), and to analyze the hydrodynamic mechanism with hydrodynamic modeling. The results show that the spatial and temporal evolution of river bars in the study area over the past 50 years exhibits an evolutionary pattern, which exhibited evident clustering distributions and significant stage-based characteristics. This pertains to the water–sediment relationships as well as hydrodynamic fluctuations. At the confluence of FR and YR, the intensity of fluvial erosion experiences a mean increment of 9.67 %, while the incoming sediment coefficient witnesses a mean reduction of 5.74 %. The position of the confluence point exhibits a close association with the evolutionary characterized of spatial clustering and temporal phasing of the river bars. The river confluence area showcases a complex turbulence structure, wherein alterations in sediment transport capacity occur due to the influence of secondary flow and the topography of the confluence area. Consequently, this impacts the flushing of river sandbars and brings about modifications in siltation. Overall, this study provides the scientific basis for YR sediment management and channel modification in response to changing runoff and sediment conditions.

Paleogeographic implication of a titanosaur eggshell from the Neogene of the Entre Ríos Province, Argentina

The Lower Member of the Ituzaingó Formation (LMIF), fluvial in origin and assigned to the Upper Miocene, contains a conglomerate level known as “Mesopotamiense” or “Conglomerado osífero” that has yielded a rich fauna of vertebrates. The aim of this contribution is to describe a titanosaurian dinosaur eggshell fragment recovered from the LMIF at the locality of Toma Vieja (western Entre Ríos Province), discussing its paleogeographic history and implications. Fragments of eggshells referred to Titanosauria are frequent from litostratigraphic units of the Upper Cretaceous of western Uruguay (e.g., Guichón, Mercedes, and Queguay Formations). Besides, a fragment of eggshell recovered from the Puerto Yeruá Formation (Upper Cretaceous) at eastern Entre Ríos Province was described. Geophysical data from the Entre Ríos Province allow to propose the presence of a Lower Cretaceous field of extensional tectonic stresses that generated structural lineaments with a E-W and ENE-WSW trend. This ancient penetrative Cretaceous tectonic framework would have exerted control on the shape of the basin and sediment flow patterns and subsequent sedimentation, by promoting the generation of accommodation space over the late Paleogene and the Neogene. The phenomenon would have conditioned the deposition of the Fray Bentos Formation, the subsequent marine Paraná Formation, and the sedimentation of the LMIF, with source materials coming from the east. Thus, it is hypothesized that the fragment of eggshell of Titanosauria would come from the eastern area of the basin (western Uruguay) as a consequence of the existence of a paleohydric system with predominantly E-W and ENE-WSW directions. This late Neogene system would have been controlled by inherited Cretaceous structural lineaments with orientations similar to those that also govern the current fluvial systems of western Uruguay, developed on the Mesozoic substrate.

Sediment runoff formation in a small periglacial catchment on the King George (Vaterloo) island, Antarctica

Global climate change has most significantly affected the Polar Regions. The increase in air temperature has stimulated the melting of glaciers in the Arctic and Antarctic, which has contributed to changes in the formation of water and sediment runoff. However, there are very few quantitative estimates of the sediment redistribution in the periglacial catchments of the Polar Regions. Specific features of water and sediment runoff were studied within the catchment area of the Korabelnyj Stream located on the Fildes Peninsula in Antarctica near the Bellingshausen Ice Dome. The main aim of the study was to investigate the conditions for the formation of water and sediment runoff and to identify the proportional contribution of washout and erosion material coming from the periglacial and maritime parts of the catchment area to the sediment runoff of the stream. A set of methods and approaches, including: a) estimates of the sediment flow connectivity index; b) fingerprinting technique; c) hydrometeorological observations; d) large-scale geomorphological survey and others, was ap[1]plied to identify the conditions for the formation of surface runoff and washout, the mechanisms of sediment redistribution in various parts of the fluvial network and to quantify the proportional contribution of two main sediment sources to the sediment runoff of the stream. A fraction with a particle size of ≤63 μm was used for geochemical and spectrometric analyzes of soils and sediments. In total, the content of 34 elements was analyzed, i.e. 6 radioisotopes and 28 stable elements. It has been established that despite the significant differences in the relief of the near-glacial and maritime parts of the catchment area, the indices of sediment connectivity are quite close and amount to –1,79 and –1,35, respectively. A significant part of the material transported by temporary streams from the slopes of the catchment area is redeposited in relief depressions partially occupied by water bodies. The main volume of sediments, which is at least 60–66% of the total sediment runoff in the outlet section of the Korabelnyj Stream, comes from the periglacial part of the catchment area. This is due to the increased water discharge relative to the non-glacial part of the catchment area, which results from the melting of snow and ice accumulated on the ice dome, the high erosion of moraine deposits unprotected by vegetation, and the presence of an ice core in moraines, which prevents water filtration.

Morfológiai vizsgálatok Magyarország délnyugati határfolyóin = Morphological Studies on South-Western Border Rivers in Hungary

Nowadays, the preservation and sustainable use of our natural values are increasingly coming to the fore, and this has implications not only for economic and field development but also for ecological aspects. In recent years, attention has shifted towards river morphological studies, which were previously relegated to the background. Understanding long-term changes and assessing the current state is essential to estimate future processes. In this article, we present our morphological studies on the Hungarian–Croatian border sections of the Mura and the Drava rivers. Historical changes were analyzed through a comparative study of historical maps from earlier periods, while the evaluation of the current state was conducted based on a detailed terrain model from a recent survey. GIS evaluation was also compared with sediment transport and flow measurement results. This comparison suggests that the morphological status of the river section under study is consistent with the typical parameters of transport processes.

Morphological properties of two-dimensional and three-dimensional bedforms in open channel flow: A flume experiments study

Bedforms are formed by sediment particles under the action of flow, which in turn affect flow and sediment movement. However, the fundamental mechanisms behind the formation and development of bedforms under varying flow conditions, the interconnection between sediment particle movement and bed morphology development, as well as the influence of bedforms on flow and sediment transport, are still not well understood. In the current study, the moveable bed load transport flume experiments under different flow conditions were done, and the development processes of two-dimensional and three-dimensional dunes formed under different flow intensities were simulated. The detailed structure of the bedforms was measured by laser scanning technology, the characteristics of the bedforms were analyzed in detail, and the relations between the formation of the bedforms and the movement of sediment particles are discussed. The results found that the correlation coefficients of the longitudinal profile curve can serve as a quick reference for distinguishing two-dimensional and three-dimensional dunes. When the crestline ratio is used as the criterion for two-dimensional and three-dimensional dunes, the relative amplitude of the dune crestline and the included angle with the flow direction should also be comprehensively considered. The lee side angles of dunes calculated using the triangle generalization method and local section tangent method are compared and show that the values obtained by the former method are only about half of that of the latter. It is also found that the lee side angles of dunes are related to the dune height. The superimposed dunes generally exist in the downstream area of the stoss side of the dunes. The local bed slopes on the stoss side of the dunes show reverse slopes. The superimposed dunes improve the local bed height and further increase the reverse slope degree of the stoss side. A streamwise ridge is an important form located in the upstream area of the dunes stoss side, and they are symmetrically distributed on both sides. Multiple streamwise ridges divide the stoss side of the dunes into relatively independent movement areas, restricting the movement of sediment particles to specific regions. According to the distribution characteristics of bed morphologies, the effects of dunes on sediment particle movement and flow energy consumption are analyzed.

Derivation of Rating Curve for Suspended Sediment Flow of River Indus at Besham

This study aims at reclaiming the huge amount of wastewater, produced from pulp and paper industry by physico-chemical treatment method following a combination of primary settling, coagulation-flocculation aided clarification (alum, lime and magnesium sulphate as coagulant) and activated carbon adsorption, in order to reduce the quantity of wastewater generation, from this water intensive industry. The chemical secondary treatment indicate the reduction in turbidity (89%), COD (84%), Total Suspended Solids (90%) and colour (89%) was obtained at the mass loading of 3400 mg l-1 of MgSO4, when 4 hours primary treated effluent was further treated by coagulation flocculation process. The combination of primary settling and lime coagulation (optimum dosage of 1400 mg l-1) resulted in effluent turbidity removal of 94%, COD reduction of 86%, TSS (Total Suspended Solids) removal of 93% and colour removal of 91.6% at initial pH of 11. The results showed that plain settling with 4 hours of retention time was effective for reducing the pollution load form pulp and board mill wastewater and this treatment step could reduce the pollution parameters up to 30%. This water could be recycled back into production process. Pilot scale study and further investigation is required before implementation of proposed treatment technology.

Identification of settling velocity with physics informed neural networks for sediment Laden flows

Physics-Informed Neural Networks (PINNs) have shown great potential in the context of fluid dynamics simulations, particularly in reconstructing flow fields and identifying key parameters. In this study, we explore the application of PINNs to recover the dimensionless settling velocity for sedimentation flow. The flow involves sediment-laden fresh water overlying salt water, which is described by Navier–Stokes equations coupled with sediment concentration and salinity transport equations. Two cases are investigated: one where the training data contains the salinity and sediment concentration fields, and another where it contains the velocity field. For both cases, we investigate several flow regimes and show that the model is capable of inferring the unknown parameter and reconstructing the hydrodynamic field of the flow. The quality of the model inference is assessed by comparing it with numerical simulations from a high-fidelity semi-Lagrangian solver. We demonstrate the model’s robustness to noise by training it with data corrupted by noise of varying magnitudes, highlighting the potential of PINNs for real-world applications.

A quasi-three-phase flow simulation of the interactions between solitary waves and a vertical seawall installed on a sandy beach

Local scour and wave loading are two key factors that affect the safety of seawalls under tsunami attacks. In this study, the scouring process at the toe of and wave impact force on a vertical seawall under consecutive solitary wave attacks are simulated using a quasi-three-phase (air, water, and sediment) flow model, which models the air and water as a fluid mixture phase and sediment as a solid phase. The air and water interface is modeled by a VOF method and the sediment–fluid interaction is modeled using the Eulerian two-phase flow method. A comparison between the beach profiles with and without the seawall shows that, with a seawall, a deeper scour hole is generated at the toe of the seawall. Besides, the presence of the seawall causes the eroded sediment to be deposited further offshore. The numerical results are then analyzed in detail regarding the flow field and sediment transport process to reveal the mechanisms of the above eroding/depositing patterns. The wave impact force on the seawall is also analyzed to understand the effect of scouring on the wave loading. It is shown that the wave impact force, despite being stochastic for a specific wave, increases in general with the deepening of the scour hole because the latter increases the exposure of the seawall to wave slamming.